Projector system for light modulation device

0001This application is a continuation of U.S. patent application Ser. No. 11/061,468 filed Feb. 22, 2005 now U.S. Pat. No. 7,226,168. The entire disclosure of the prior application is hereby incorporated by reference in its entirety.

BACKGROUND

0002Aspects of the invention can relate to a projector that projects an image with the use of a liquid crystal display panel or any other type of light modulation device.

0003As an illumination device for a liquid crystal display panel incorporated into a projector in the related art, a type in which a light-source light from a white light source is separated into lights of three colors and relay lenses are disposed in illumination optical paths for two colors, so that efficiency for utilization of illumination of respective colors is improved by compensating for a difference of optical path lengths with respect to the remaining one color can be used. See, for example, JP-A-1-243014.

SUMMARY

0004In the related art projector described above, however, identical optical systems including lenses having the same radius of curvature or the like can be incorporated into a pair of illumination optical paths into which the relay lenses are incorporated. This causes illumination areas projected onto the liquid crystal light valves for respective colors to vary in size with a difference of the wavelength characteristics between the two illumination optical paths. Such a difference in size among the illumination areas will produce a colored display shadow on the fringe of a projected image, and possibly results in a failure.

0005An object of the invention can be to provide a projector capable of projecting a high-quality image by illumination that does not produce a difference in size among illumination areas for respective colors including red (R), green (G), and blue (B).

0006An exemplary projector of the invention can include a color separation system to cause illumination lights of first through third colors to branch from a light-source light emitted from a light source and guide the illumination lights of the first through third colors to first through third optical paths, respectively, and first through third light modulation devices to be illuminated, respectively, by the illumination lights of the first through third colors and independently modulate the illumination lights of their respective colors. A distance from the light source to the third light modulation device can be different from a distance from the light source to the first light modulation device and a distance from the light source to the second light modulation device, and a relay system can be disposed in each of the first and second optical paths or in the third optical path alone. Also, a correcting system to correct a chromatic aberration that gives an influence to sizes of illumination areas, for at least the first color and the second color when an angle distribution of the illumination lights of the first through third colors that respectively go incident on the first through third light modulation devices is adjusted, is disposed in the first through third optical paths.

0007In the exemplary projector described above, the correcting system corrects a chromatic aberration that gives an influence to sizes of illumination areas, for at least the first color and the second color. Hence, at least the first and second light modulation devices are illuminated by illumination areas of the same size. It is thus possible to prevent a display shadow from being produced on the fringe of a projected image or reduce the production of such a display shadow, which in turn enables a high-quality image to be projected.

0008A chromatic aberration that gives an influence to sizes of illumination areas can refer to a chromatic aberration (a chromatic aberration of magnification and a longitudinal chromatic aberration) induced by all or part of lenses (including a concave mirror and a lens array) disposed in optical paths from the light source to the light modulation devices. Hereinafter, a chromatic aberration that gives an influence to sizes of illumination areas can refer to as a chromatic aberration.

0009According to an aspect of the invention, in the exemplary projector, the correcting system can include first and second field lenses each having a different refractive power with respect to a reference wavelength and disposed, respectively, in the first and second optical paths oppositely to light-incident surface sides of the first and second light modulation devices, and a third field lens disposed in the third optical path oppositely to a light-incident surface side of the third light modulation device. In this case, by setting refractive powers of the first and second field lenses disposed, respectively, in the optical paths of illumination lights of the first and second colors and having the same length of optical path from the light source to the light modulation device, it is possible to illuminate the first and second light modulation devices by illumination areas of the same size.

0010According to another aspect of the invention, the refractive power of the first field lens for the first color can be almost equal to the refractive power of the second field lens for the second color. In this case, an aberration can be corrected mutually for illumination lights of first and second colors.

0011According to still another aspect of the invention, the relay system can be disposed in the third optical path. In this case, the need to dispose the relay systems in the first and second optical paths is eliminated, and the illumination device can be of a simple structure.

0012According to still another aspect of the invention, the first and second field lenses can be planoconvex lenses having flat surfaces, respectively, on sides of the first and second light modulation devices. In this case, it is possible to adjust an angle of incidence with respect to the first and second light modulation devices to achieve satisfactory properties.

0013According to still another aspect of the invention, with the first through third colors being blue, green, and red, respectively, and Rb and Rg being radii of curvature of the first and second field lenses, respectively, an inequality as follows is satisfied: Rb>Rg. In this case, red can serve as a relay system, and color correction between green and blue with the use of curvatures of the field lenses can be achieved.

0014The radius of curvature referred to herein can mean the radius of curvature of a convex surface when the field lens is a planoconvex lens. When the both surfaces of the field lens are curved surfaces, the field lens is replaced with a virtual planoconvex lens having the same refractive power, and the radius of curvature can mean the radius curvature of the convex surface of this virtual planoconvex lens. The same applies to the description below. When the both surfaces of the field lens are in the shape of a lens, the radius of curvature, R, is given as an approximation by an equation as follows: <br /><i>R=R</i>1×<i>R</i>2(<i>R</i>1+<i>R</i>2),<br /> where R<b>1</b> is the absolute value of the radius of curvature of the first surface of the field lens, and R<b>2</b> is the absolute value of the radius of curvature of the second surface.

0015According to still another aspect of the invention, with Rr being a radius of curvature of the third field lens, an inequality as follows is satisfied: Rg≧Rr. In this case, it is possible to correct a chromatic aberration for red resulted from the relay system.

0016According to still another aspect of the invention, with the first through third colors being red, green, and blue, respectively, and Rr and Rg being radii of curvature of the first and second field lenses, respectively, an inequality as follows can be satisfied: Rg>Rr. In this case, blue can serve as a relay system, and color correction between green and red with the use of curvatures of the field lenses can be achieved.

0017According to still another aspect of the invention, with Rb being a radius of curvature of the third field lens, then an inequality as follows can be satisfied: Rr≧Rb. In this case, it is possible to correct a chromatic aberration for blue resulted from the relay system.

0018According to still another aspect of the invention, with the first through third colors being blue, red, and green, respectively, and Rb and Rr being radii of curvature of the first and second field lenses, respectively, an inequality as follows can be satisfied: Rb>Rr. In this case, green serves as a relay system, and color correction between blue and red with the use of curvatures of the field lenses can be achieved.

0019According to still another aspect of the invention, with Rg being a radius of curvature of the third field lens, an inequality as follows can be satisfied: Rr≧Rg. In this case, a chromatic aberration for green resulted from the relay system can be corrected.

0020According to still another aspect of the invention, the relay system is disposed in each of the first and second optical paths. In this case, it is possible to shorten the overall distance from the light source to the light modulation devices.

0021According to still another aspect of the invention, the third field lens can be a planoconvex lens having a flat surface on a side of the third light modulation device. In this case, it is possible to adjust an angle of incidence with respect to the third light modulation device to achieve satisfactory properties.

0022According to still another aspect of the invention, with the first through third colors being red, blue, and green, respectively, and Rr and Rb being radii of curvature of the first and second field lenses, respectively, then an inequality as follows can be satisfied: Rb>Rr. In this case, red and blue serve as relay systems, and color correction between red and blue with the use of curvatures of the field lenses can be achieved.

0023According to still another aspect of the invention, with Rg being a radius of curvature of the third field lens, an inequality as follows can be satisfied: Rg≧Rb. In this case, it is possible to correct a relative chromatic aberration with respect to green resulted from the absence of the relay system.

0024According to still another aspect of the invention, with the first through third colors be red, green, and blue, respectively, and Rr and Rg being radii of curvature of the first and second field lenses, respectively, an inequality as follows can be satisfied: Rg>Rr. In this case, red and green can serve as relay systems, and color correction between red and green with the use of the curvatures of the field lenses can be achieved.

0025According to still another aspect of the invention, with Rb being a radius of curvature of the third field lens, an inequality as follows can be satisfied: Rb>Rg. In this case, it is possible to correct a relative chromatic aberration with respect to blue resulted from the absence of the relay system.

0026According to still another aspect of the invention, with the first through third colors being green, blue, and red, respectively, and Rg and Rb being radii of curvature of the first and second field lenses, respectively, an inequality as follows can be satisfied: Rb>Rg. In this case, green and blue can serve as relay systems, and color correction between green and blue with the use of curvatures of the field lenses can be achieved.

0027According to still another aspect of the invention, with Rr being a radius of curvature of the third field lens, an inequality as follows can be satisfied: Rr≧Rb. In this case, it is possible to correct a relative chromatic aberration with respect to red resulted from the absence of the relay system.

0028According to still another aspect of the invention, a light combining member to combine and emit image lights of respective colors from the first through third light modulation devices, and a projection system to project the image lights that have been combined by passing through the light combining system are further included. In this case, the light modulation devices can be illuminated by illumination in which illumination areas are matched for at least the first and second light modulation devices. A high-quality color combined image having fewer display shadows can be thus projected.

BRIEF DESCRIPTION OF THE DRAWINGS

0029The invention will be described with reference to the accompanying drawings, wherein like numerals reference like elements, and wherein:

0030<figref idref="DRAWINGS">FIG. 1</figref> is a view used to describe optical systems in a projector according to a first exemplary embodiment of the invention;

0031<figref idref="DRAWINGS">FIG. 2</figref> is a view used to describe optical systems in a projector according to a second exemplary embodiment of the invention;

0032<figref idref="DRAWINGS">FIG. 3</figref> is a view used to describe optical systems in a projector according to a third exemplary embodiment of the invention;

0033<figref idref="DRAWINGS">FIG. 4</figref> is a view used to describe optical systems in a projector according to a fourth exemplary embodiment of the invention;

0034<figref idref="DRAWINGS">FIG. 5</figref> is a view used to describe optical systems in a projector according to a fifth exemplary embodiment of the invention; and

0035<figref idref="DRAWINGS">FIG. 6</figref> is a view used to describe optical systems in a projector according to a sixth exemplary embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

0036Hereinafter, the structure of a projector according to a first exemplary embodiment of the invention will be described with reference to an accompanying drawing.

0037<figref idref="DRAWINGS">FIG. 1</figref> is an exemplary block diagram used to describe optical systems in the projector of this embodiment. A projector <b>10</b> can include a light source <b>21</b> to generate a light-source light, a color separation system <b>23</b> to separate a light-source light from the light source <b>21</b> into lights of three colors including red, green and blue, a light modulation portion <b>25</b> illuminated by illumination lights of respective colors emitted from the color separation system <b>23</b>, a cross dichroic prism <b>27</b> to combine image lights of respective colors from the light modulation portion <b>25</b>, and a projection lens <b>29</b> serving as a projection system to project image lights that have passed through the cross dichroic prism <b>27</b> onto a screen (not shown).

0038The light source <b>21</b> can include a light source lamp <b>21</b><i>a, </i>a concave lens <b>21</b><i>b, </i>a pair of fly's-eye systems <b>21</b><i>d </i>and <b>21</b><i>e, </i>a polarization converting member <b>21</b><i>g, </i>and a superimposing lens <b>21</b><i>i. </i>Of these components, the light source lamp <b>21</b><i>a </i>can include, for example, a high pressure mercury-vapor lamp, and is provided with a concave mirror that collects light-source lights to be emitted forward. The concave lens <b>21</b><i>b </i>plays a role in making light-source lights from the light source lamp <b>21</b><i>a </i>parallel. The concave lens <b>21</b><i>b </i>can obtain parallel light beams when the concave mirror is of a sphere or an ellipsoid; however, it can be omitted when the concave mirror is a parabolic mirror.

0039The pair of fly's-eye systems <b>21</b><i>d </i>and <b>21</b><i>e </i>can include plural element lenses arrayed in a matrix fashion, and these element lenses separate light-source lights from the light source lamp <b>21</b><i>a </i>having passed through the concave lens <b>21</b><i>b </i>to be independently collected or diffused. The polarization converting member <b>21</b><i>g </i>converts light-source lights emitted from the fly's-eye system <b>21</b><i>e, </i>for example, to only S-polarized components perpendicular to the sheet surface of <figref idref="DRAWINGS">FIG. 1</figref>, which are supplied to an optical system in the following stage. The superimposing lens <b>21</b><i>i </i>enables superimposed illumination for the light modulation devices for respective colors provided in the light modulation portion <b>25</b> by forcing the illumination lights having passed through the polarization converting member <b>21</b><i>g </i>to be converged as a whole as needed. In other words, illumination lights that have passed through the both fly's-eye systems <b>21</b><i>d </i>and <b>21</b><i>e </i>and the superimposing lens <b>21</b><i>i </i>pass through the color separation system <b>23</b>, which will be described in detail below, and are superimposed to illuminate homogeneously the light modulation devices for respective colors, that is, liquid crystal light valves <b>25</b><i>a, </i><b>25</b><i>b, </i>and <b>25</b><i>c, </i>provided in the light modulation portion <b>25</b>.

0040The color separation system <b>23</b> can include first and second dichroic mirrors <b>23</b><i>a </i>and <b>23</b><i>b, </i>three field lenses <b>23</b><i>f, </i><b>23</b><i>g, </i>and <b>23</b><i>h </i>serving as correcting systems, and reflection mirrors, <b>23</b><i>j, </i><b>23</b><i>m, </i><b>23</b><i>n, </i>and <b>23</b><i>o, </i>and constitutes an illumination device together with the light source <b>21</b>. Of the lights of three colors including red, green, and blue, the first dichroic mirror <b>23</b><i>a </i>reflects a red light and a green light and transmits a blue light. Of the incident lights of two colors including red and green, the second dichroic mirror <b>23</b><i>b </i>reflects the green light and transmits the red light.

0041In the color separation system <b>23</b>, a substantially white light-source light from the light source <b>21</b> is deflected by the reflection mirror <b>23</b><i>j </i>to go incident on the first dichroic mirror <b>23</b><i>a. </i>The blue light having passed through the first dichroic mirror <b>23</b><i>a </i>goes incident on the field lens <b>23</b><i>f </i>by way of the reflection mirror <b>23</b><i>m </i>while remaining intact, for example, in the form of an S-polarized light. The green light, having been reflected on the first dichroic mirror <b>23</b><i>a </i>and further on the second dichroic mirror <b>23</b><i>b, </i>goes incident on the field lens <b>23</b><i>g </i>while remaining intact, for example, in the form of an S-polarized light. Further, the red light having passed through the second dichroic mirror <b>23</b><i>b </i>goes incident on the field lens <b>23</b><i>h </i>for use in adjusting an angle of incidence by way of lenses LL<b>1</b> and LL<b>2</b> and the reflection mirrors <b>23</b><i>n </i>and <b>23</b><i>o </i>while remaining intact, for example, in the form of an S-polarized light. The lenses LL<b>1</b> and LL<b>2</b> and the field lens <b>23</b><i>h </i>together constitute a relay system.

0042The relay system is furnished with a function of delivering an image from the first lens LL<b>1</b> almost intact to the field lens <b>23</b><i>h </i>via the second lens LL<b>2</b>. A distance from the light source <b>21</b> to the liquid crystal light valve <b>25</b><i>c </i>is longer than distances from the light source <b>21</b> to the liquid crystal light valves <b>25</b><i>a </i>and <b>25</b><i>b. </i>However, by disposing the relay system in an optical path OP<b>3</b>, it is possible to prevent, to some extent, a decrease in efficiency for light utilization caused by light diffusion or the like induced from such a difference among optical paths.

0043The light modulation portion <b>25</b> can include three liquid crystal light valves <b>25</b><i>a </i>through <b>25</b><i>c </i>each serving as a light modulation device, and three pairs of polarizing filters <b>25</b><i>e, </i><b>25</b><i>f, </i>and <b>25</b><i>g </i>that are disposed to sandwich the liquid crystal light valves <b>25</b><i>a </i>through <b>25</b><i>c, </i>respectively. The blue light branched by passing through the first dichroic mirror <b>23</b><i>a </i>in the color separation system <b>23</b> goes incident on the first liquid crystal light valve <b>25</b><i>a </i>for blue lights via the field lens <b>23</b><i>f. </i>The green light branched by being reflected on the second dichroic mirror <b>23</b><i>b </i>in the color separation system <b>23</b> goes incident on the second liquid crystal light valve <b>25</b><i>b </i>for green lights via the field lens <b>23</b><i>g. </i>The red light branched by passing through the second dichroic mirror <b>23</b><i>b </i>goes incident on the third liquid crystal light valve <b>25</b><i>c </i>for red lights via the field lens <b>23</b><i>h. </i>

0044Each of the liquid crystal light valves <b>25</b><i>a </i>through <b>25</b><i>c </i>can be a non-luminous light modulation device that modulates a spatial intensity distribution of an incident illumination light. Lights of three colors that come incident on the respective liquid crystal light valves <b>25</b><i>a </i>through <b>25</b><i>c </i>are modulated in response to driving signals or image signals inputted into the respective liquid crystal light valves <b>25</b><i>a </i>through <b>25</b><i>c </i>as electrical signals. In this instance, the polarizing filters <b>25</b><i>e, </i><b>25</b><i>f, </i>and <b>25</b><i>g </i>not only adjust the polarization directions of illumination lights to go incident on the respective liquid crystal light valves <b>25</b><i>a </i>through <b>25</b><i>c, </i>but also take out, as image lights, component lights in a specific polarization direction from modulated lights emitted from the respective liquid crystal light valves <b>25</b><i>a </i>through <b>25</b><i>c. </i>

0045The cross dichroic prism <b>27</b> is a light combining member, and can include two kinds of dielectric multi-layer films <b>27</b><i>a </i>and <b>27</b><i>b </i>formed in the shape of a capital X. In the cross dichroic prism <b>27</b> of this embodiment, a dielectric multi-layer film <b>27</b><i>a </i>for reflecting blue lights and a dielectric multi-layer film <b>27</b><i>b </i>for reflecting red lights are incorporated so as to cross with each other at right angles. The cross dichroic prism <b>27</b> emits a blue image light from the liquid crystal light valve <b>25</b><i>a </i>to the right in the traveling direction by reflecting the blue image light on the dielectric multi-layer film <b>27</b><i>a, </i>and emits a green image light from the liquid crystal light valve <b>25</b><i>b </i>to travel straight via the dielectric multi-layer films <b>27</b><i>a </i>and <b>27</b><i>b </i>while emitting a red image light from the liquid crystal light valve <b>25</b><i>c </i>to the left in the traveling direction by reflecting the red image light on the dielectric multi-layer film <b>27</b><i>b. </i>

0046The projection lens <b>29</b> can project color image lights combined by the cross dichroic prism <b>27</b> onto a screen (not shown) at a desired fixed scaling factor or within a desired scaling range. In other words, a color moving image or a color still image at a desired scaling factor corresponding to driving signals or image signals inputted into the respective light valves <b>25</b><i>a </i>through <b>25</b><i>c </i>is projected at a desired scaling factor.

0047The color separation system <b>23</b> in the projector <b>10</b> as described above will now be described in detail. In the color separation system <b>23</b>, a first optical path OP<b>1</b> that passes through the first dichroic mirror <b>23</b><i>a </i>to travel toward the field lens <b>23</b><i>f </i>serves as an optical path for blue lights, that is, a first color, as has been described. In addition, a second optical path OP<b>2</b> that is reflected on the first dichroic mirror <b>23</b><i>a </i>and is reflected on the second dichroic mirror <b>23</b><i>b </i>to travel toward the field lens <b>23</b><i>g </i>serves as an optical path for green lights, that is, a second color, as has been described above. Further, a third optical path OP<b>3</b> that passes through the first and second dichroic mirrors <b>23</b><i>a </i>and <b>23</b><i>b </i>to travel toward the field lens <b>23</b><i>h </i>serves as an optical path for red lights as a third color.

0048In the color separation system <b>23</b> of this exemplary embodiment, the first field lens <b>23</b><i>f </i>disposed in the first optical path OP<b>1</b> for blue lights and the second field lens <b>23</b><i>g </i>disposed in the second optical path OP<b>2</b> for green lights comprise similar planoconvex lenses because of symmetry properties of the optical paths. Meanwhile, the third field lens <b>23</b><i>h </i>disposed in the third optical path OP<b>3</b> for red lights can include a biconvex lens by taking image-forming characteristics of the lenses LL<b>1</b> and LL<b>2</b> or the like into account.

0049In addition, in this exemplary embodiment, with Rb, Rg, and Rr being the radii of curvature of the field lenses <b>23</b><i>f, </i><b>23</b><i>g, </i>and <b>23</b><i>h, </i>respectively, an inequality as follows is satisfied: <br />Rb>Rg≧Rr  (1)

0050In this exemplary embodiment, both the first and second field lenses <b>23</b><i>f </i>and <b>23</b><i>g </i>can include planoconvex lenses. However, one or both of the two field lenses <b>23</b><i>f </i>and <b>23</b><i>g </i>may comprise biconvex lenses.

0051In this exemplary embodiment, because an inequality, Rb>Rg, is satisfied, a refractive power at the same reference wavelength (for example, g-line) can be smaller in the first field lens <b>23</b><i>f </i>than in the second field lens <b>23</b><i>g. </i>Further, under these conditions, it is possible to make a refractive power of the first field lens <b>23</b><i>f </i>for blue lights equal to a refractive power of the second field lens <b>23</b><i>g </i>for green lights. In this case, because a chromatic aberration is corrected for blue and green, both the liquid crystal light valves <b>25</b><i>a </i>and <b>25</b><i>b </i>are illuminated by illumination areas of the same size.

0052Further, because an inequality, Rg≧Rr, is satisfied, it is possible to make a refractive power of the third field lens <b>23</b><i>h </i>for red lights equal to or greater than a refractive power of the second field lens <b>23</b><i>g </i>for green lights. This makes it possible to correct a chromatic aberration for red and green or the like, too. The configuration described above makes it possible to illuminate the respective liquid crystal light valves <b>25</b><i>a, </i><b>25</b><i>b, </i>and <b>25</b><i>c </i>by illumination areas of the same size, and light modulation areas for respective colors provided in the respective liquid crystal light valves <b>25</b><i>a </i>through <b>25</b><i>c </i>are thereby illuminated, respectively, by illumination lights of red, green, and blue of the same size in agreement. It is thus possible to prevent or reduce a colored display shadow from being produced on the fringe of an image projected onto the screen by the projection lens <b>29</b>, which in turn enables a high-quality image to be projected.

0053The radius of curvature of each of the field lenses <b>23</b><i>f, </i><b>23</b><i>g, </i>and <b>23</b><i>h </i>will now be described in greater detail. In an exemplary manufacturing example, the ratio of the radii of curvature, Rb, Rg, and Rr, of the field lenses <b>23</b><i>f, </i><b>23</b><i>g, </i>and <b>23</b><i>h, </i>respectively, is set as follows: Rb:Rg:Rr=1.2:1.0:0.4. This configuration makes it possible to bring illumination areas for respective colors including red, green, and blue into exact agreement, which can in turn prevent a display shadow from being produced on the fringe of a projected image.

0054Operations of the projector <b>10</b> of this exemplary embodiment will now be described. A light-source light from the light source <b>21</b> can be separated into color lights by the first and second dichroic mirrors <b>23</b><i>a </i>and <b>23</b><i>b </i>provided in the color separation system <b>23</b> to independently go incident on the corresponding liquid crystal light valves <b>25</b><i>a </i>through <b>25</b><i>c </i>as illumination lights. Each of the liquid crystal light valves <b>25</b><i>a </i>through <b>25</b><i>c </i>has a two-dimensional refractive power distribution because its state varies with an image signal from the outside, and thereby modulates an illumination light in a two-dimensional space pixel by pixel. The illumination lights modulated in the respective liquid crystal light valves <b>25</b><i>a </i>through <b>25</b><i>c </i>in this manner, that is, image lights of respective colors, are combined in the cross dichroic prism <b>27</b> and then go incident on the projection lens <b>29</b>. The image lights that come incident on the projection lens <b>29</b> are projected onto the unillustrated screen as a color image. In this instance, a mutual chromatic aberration is corrected by adjusting, as needed, the radii of curvature, Rb, Rg, and Rr, of the respective field lenses <b>23</b><i>f, </i><b>23</b><i>g, </i>and <b>23</b><i>h </i>provided in the color separation system <b>23</b> for use in adjusting angles of incidence of illumination lights with respect to the respective liquid crystal light valves <b>25</b><i>a </i>through <b>25</b><i>c. </i>Hence, the respective liquid crystal light valves <b>25</b><i>a </i>through <b>25</b><i>c </i>can be illuminated by illumination areas of exactly the same size without any waste. It is thus possible to project and display a high-quality color image having no display shadow.

0055In the projector <b>10</b> of the first exemplary embodiment as described above, of the lengths of the optical paths of illumination lights of respective colors (lengths of the optical paths from the light source <b>21</b> to the respective liquid crystal light valves <b>25</b><i>a </i>through <b>25</b><i>c</i>), the lengths of the optical paths for blue lights and green lights are made equal, whereas the length of the optical path for red lights is made longer than the others.

0056On the contrary, in a projector <b>10</b>A of this exemplary embodiment, as is shown in <figref idref="DRAWINGS">FIG. 2</figref>, the length of the optical path for blue lights is made longer than the lengths of the optical paths for red lights and green lights. In addition, the lengths of the optical paths for red lights and green lights are made equal, while the relay system is inserted in the optical path for blue lights. The projector <b>10</b>A of this exemplary embodiment is different from the counterpart of the first exemplary embodiment in displacement of color lights; however, other than this difference, it is configured in the same manner as the counterpart of the first exemplary embodiment.

0057In this exemplary embodiment, the first field lens <b>23</b><i>f </i>disposed in the first optical path OP<b>1</b> for red lights and the second field lens <b>23</b><i>g </i>disposed in the second optical path OP<b>2</b> for green lights comprise similar planoconvex lenses. Meanwhile, the third field lens <b>23</b><i>h </i>disposed in the third optical path OP<b>3</b> for blue lights comprises a biconvex lens to be matched with the relay system in terms of image-forming characteristics or the like. Also, let Rr, Rg, and Rb be the radii of curvature of the first through third field lenses, respectively, then an inequality as follows is satisfied: <br />Rg>Rr≧Rb  (2)<br /> In this exemplary embodiment, both the first and second field lenses comprise planoconvex lenses. However, one or both of the two field lenses can include biconvex lenses.

0058In this exemplary embodiment, because an inequality, Rg>Rr, is satisfied, it is possible to make a refractive power of the first field lens <b>23</b><i>f </i>for red lights equal to a refractive power of the second field lens <b>23</b><i>g </i>for green lights, which makes it possible to correct a chromatic aberration for red and green. Also, because an inequality, Rr≧Rb, is satisfied, it is possible to match a refractive power of the third field lens <b>23</b><i>h </i>for blue lights with an illumination area having passed through the second field lens <b>23</b><i>g </i>for green lights. The configuration as described above makes it possible to correct a chromatic aberration for respective colors including red, green, and blue, and the respective liquid crystal light valves <b>25</b><i>a, </i><b>25</b><i>b, </i>and <b>25</b><i>c </i>are thereby illuminated by illumination areas of the same size. It is thus possible to project a high-quality image by preventing or reducing a display shadow from being produced.

0059In a projector <b>10</b>B of a third exemplary embodiment, as is shown in <figref idref="DRAWINGS">FIG. 3</figref>, of the lengths of the optical paths of illumination lights of respective colors (lengths of the optical paths from the light source <b>21</b> to the respective liquid crystal light valves <b>25</b><i>a </i>through <b>25</b><i>c</i>), the length of the optical path for green lights is made longer than the lengths of the optical paths for blue lights and red lights. In addition, the lengths of the optical paths for blue lights and red light can be made equal, while the relay system is inserted in the optical path for green lights. The projector <b>10</b>B of this embodiment is different from the counterpart of the first exemplary embodiment in displacement of color lights; however, other than this difference, it is configured in the same manner as the counterpart of the first exemplary embodiment.

0060In this exemplary embodiment, the first field lens <b>23</b><i>f </i>disposed in the first optical path OP<b>1</b> for blue lights and the second field lens <b>23</b><i>g </i>disposed in the second optical path OP<b>2</b> for red lights can include similar planoconvex lenses. Meanwhile, the third field lens <b>23</b><i>h </i>disposed in the third optical path OP<b>3</b> for green lights comprises a biconvex lens to be matched with the relay system in terms of image-forming characteristic or the like. In addition, let Rb, Rr, and Rg be the radii of curvature of the first through third field lenses, respectively, then an inequality as follows is satisfied: <br />Rb>Rr≧Rg  (3)<br /> In this embodiment, both the first and second field lenses can include planoconvex lenses. However, one or both of the two field lenses can include biconvex lenses.

0061In this exemplary embodiment, because an inequality, Rb>Rr, is satisfied, it is possible to make a refractive power of the first field lens <b>23</b><i>f </i>for blue lights equal to a refractive power of the second field lens <b>23</b><i>g </i>for red lights, which makes it possible to correct a chromatic aberration for blue and red. Likewise, because an inequality, Rr≧Rg, is satisfied, it is possible to match a refractive power of the third field lens <b>23</b><i>h </i>for green lights with an illumination area having passed through the second field lens <b>23</b><i>g </i>for red lights. The configuration as described above makes it possible to correct a chromatic aberration for respective colors including red, green, and blue, and the respective liquid crystal light valves <b>25</b><i>a, </i><b>25</b><i>b, </i>and <b>25</b><i>c </i>are thereby illuminated by illumination areas of the same size. It is thus possible to project a high-quality image by preventing a display shadow from being produced.

0062Hereinafter, the structure of a projector according to a fourth exemplary embodiment will be described with reference to an accompanying drawing.

0063<figref idref="DRAWINGS">FIG. 4</figref> is an exemplary block diagram used to describe optical systems in the projector of this embodiment. A projector <b>110</b> is a modification of the projector <b>10</b> of the first exemplary embodiment shown in <figref idref="DRAWINGS">FIG. 1</figref>, in which the color separation system <b>23</b> is modified, and no particular modification is added to the light source <b>21</b>, the light modulation portion <b>25</b>, the cross dichroic prism <b>27</b>, and the projection lens <b>29</b>.

0064In the projector <b>110</b>, a color separation system <b>123</b> can include a cross dichroic mirror having two dichroic mirrors <b>123</b><i>a </i>and <b>123</b><i>b </i>that intersect with each other in the shape of a capital X, three field lenses <b>23</b><i>g, </i><b>123</b><i>h, </i>and <b>223</b><i>h, </i>lenses LL<b>1</b> and LL<b>2</b>, and reflection mirrors <b>123</b><i>n </i>and <b>123</b><i>o. </i>Of the lights of three colors including red, green, and blue, the first dichroic mirror <b>123</b><i>a </i>reflects a red light and transmits a blue light and a green light. In addition, the second dichroic mirror <b>123</b><i>b </i>reflects a blue light and transmits a red light and a green light. In the color separation system <b>123</b>, a substantially white light-source light from the light source <b>21</b> goes incident on the cross dichroic mirrors <b>123</b><i>a </i>and <b>123</b><i>b. </i>The green light that has passed through the cross dichroic mirrors <b>123</b><i>a </i>and <b>123</b><i>b </i>goes incident on the third field lens <b>23</b><i>g </i>for use in adjusting an angle of incidence while remaining intact. The red light reflected on the first dichroic mirror <b>123</b><i>a </i>goes incident on the first field lens <b>123</b><i>h </i>for use in adjusting an angle of incidence by way of the lenses LL<b>1</b> and LL<b>2</b> and the reflection mirrors <b>123</b><i>n </i>and <b>123</b><i>o. </i>Further, the blue light reflected on the second dichroic mirror <b>123</b><i>b </i>goes incident on the second field lens <b>223</b><i>h </i>for use in adjusting an angle of incidence by way of the lenses LL<b>1</b> and LL<b>2</b> and the reflection mirrors <b>123</b><i>n </i>and <b>123</b><i>o. </i>In the first optical path OP<b>1</b> and the second optical path OP<b>2</b>, the lenses LL<b>1</b> and LL<b>2</b> and the field lenses <b>123</b><i>h </i>and <b>223</b><i>h </i>constitute relay systems.

0065Each relay system can be furnished with a function of delivering an image from the first lens LL<b>1</b> intact to the field lens <b>123</b><i>h/</i><b>223</b><i>h </i>via the second lens LL<b>2</b>. Distances from the light source <b>21</b> to the two liquid crystal light valves <b>25</b><i>a </i>and <b>25</b><i>c </i>are longer than a distance from the light source <b>21</b> to the liquid crystal light valve <b>25</b><i>b. </i>However, by disposing the relay systems in the optical paths OP<b>1</b> and OP<b>2</b>, it is possible to prevent or reduce, to some extent, a decrease in efficiency for light utilization caused by light diffusion or the like induced by such a difference of optical paths.

0066In the color separation system <b>123</b> as described above, the third field lens <b>23</b><i>g </i>disposed in the third optical path OP<b>3</b> for green lights can include a planoconvex lens. Meanwhile, the first and second field lenses <b>123</b><i>h </i>and <b>223</b><i>h </i>disposed, respectively, in the first optical path OP<b>1</b> for red lights and the second optical path OP<b>2</b> for blue lights can include biconvex lenses by taking image-forming characteristics of the lenses LL<b>1</b> and LL<b>2</b> into account.

0067Let Rr, Rb, and Rg be the radii of curvature of the first through third field lenses <b>123</b><i>h, </i><b>223</b><i>h, </i>and <b>23</b><i>g, </i>respectively, then an inequality as follows is satisfied: <br />Rg≧Rb>Rr  (4)

0068In this exemplary embodiment, the third field lens <b>23</b><i>g </i>can include a planoconvex lens. However, the third field lens <b>23</b><i>g </i>can include a biconvex lens.

0069In this exemplary embodiment, because an inequality, Rb>Rr, is satisfied, a refractive power at the same reference wavelength is larger in the first field lens <b>123</b><i>h </i>for red lights than in the second field lens <b>223</b><i>h </i>for blue lights. Further, under these conditions, it is possible to make a refractive power of the first field lens <b>123</b><i>h </i>for red lights equal to a refractive power of the second field lens <b>223</b><i>h </i>for blue lights. In this case, because a chromatic aberration is corrected for red and blue, both the liquid crystal light valves <b>25</b><i>a </i>and <b>25</b><i>c </i>are illuminated by illumination areas of the same size. Further, because an inequality, Rg≧Rb, is satisfied in this exemplary embodiment, it is possible to make a refractive power of the third field lens <b>23</b><i>g </i>for green lights equal to or smaller than a refractive power of the second field lens <b>223</b><i>h </i>for blue lights or the like. This makes it possible to correct a chromatic aberration for green and blue or the like, too. The configuration as described above makes it possible to illuminate the respective liquid crystal light valves <b>25</b><i>a, </i><b>25</b><i>b, </i>and <b>25</b><i>c </i>by illumination areas of the same size, and light modulation areas for respective colors provided in the respective liquid crystal light valves <b>25</b><i>a </i>through <b>25</b><i>c </i>are thereby illuminated, respectively, by illumination lights of red, green, and blue of the same size in agreement. It is thus possible to prevent or reduce a display shadow from being produced on the image projected onto the screen by the projection lens <b>29</b>, which in turn enables a high-quality image to be projected.

0070In the projector <b>110</b> of the fourth exemplary embodiment as described above, of the lengths of the optical paths of illumination lights of respective colors (lengths of the optical paths from the light source <b>21</b> to the respective liquid crystal light valves <b>25</b><i>a </i>through <b>25</b><i>c</i>), the lengths of the optical paths for red lights and blue lights are made equal, and made longer than the length of the optical path for green lights. On the contrary, in a projector <b>110</b>A of this exemplary embodiment, as is shown in <figref idref="DRAWINGS">FIG. 5</figref>, the lengths of the optical paths for red lights and green lights are made longer than the length of the optical path for blue lights. In addition, the lengths of the optical paths for red lights and green lights are made equal, while the relay system is inserted in each of the optical paths. The projector <b>110</b>A of this exemplary embodiment is different from the counterpart of the fourth exemplary embodiment in displacement of color lights; however, other than this difference, it is configured in the same manner as the counterpart of the fourth exemplary embodiment.

0071In this exemplary embodiment, the third field lens <b>23</b><i>g </i>disposed in the third optical path OP<b>3</b> for blue lights comprises a planoconvex lens. Meanwhile, the first field lens <b>123</b><i>h </i>disposed in the first optical path OP<b>1</b> for red lights and the second field lens <b>223</b><i>h </i>disposed in the second optical path OP<b>2</b> for green lights comprise biconvex lenses to be matched with the relay systems in terms of image-forming characteristics or the like. Also, let Rr, Rg, and Rb be the radii of curvature of the first through third field lenses, respectively, then an inequality as follows is satisfied: <br />Rb>Rg>Rr  (5)<br /> In this exemplary embodiment, the third field lens <b>23</b><i>g </i>comprises a planoconvex lens. However, it can include a biconvex lens.

0072In this exemplary embodiment, because an inequality, Rg>Rr, is satisfied, it is possible to make a refractive power of the first field lens <b>123</b><i>h </i>for red lights equal to a refractive power of the second field lens <b>223</b><i>h </i>for green lights, which makes it possible to correct a chromatic aberration for red and green. Likewise, because an inequality, Rb>Rg, is satisfied, it is possible to make a refractive power of the third field lens <b>23</b><i>g </i>for blue lights equal to or smaller than a refractive power of the second field lens <b>223</b><i>h </i>for green lights or the like. The configuration as described above makes it possible to correct a chromatic aberration for respective colors including red, green, and blue, and the respective liquid crystal light valves <b>25</b><i>a, </i><b>25</b><i>b, </i>and <b>25</b><i>c </i>are thereby illuminated by illumination areas of the same size. It is thus possible to project a high-quality image by preventing or reducing a display shadow from being produced.

0073In a projector <b>110</b>B of a sixth exemplary embodiment, as is shown in <figref idref="DRAWINGS">FIG. 6</figref>, of the lengths of the optical paths of illumination lights of respective colors (lengths of the optical paths from the light source <b>21</b> to the respective liquid crystal light valves <b>25</b><i>a </i>through <b>25</b><i>c</i>), the lengths of the optical paths for green lights and blue lights are made longer than the length of the optical path for red lights. In addition, the lengths of the optical paths for green lights and blue lights are made equal, while the relay system is inserted in each of the optical paths. The projector <b>110</b>B of this exemplary embodiment is different from the counterpart of the fourth exemplary embodiment in displacement of color lights; however, other than this difference, it is configured in the same manner as the counterpart of the fourth exemplary embodiment.

0074In this exemplary embodiment, the third field lens <b>23</b><i>g </i>disposed in the third optical path OP<b>3</b> for red lights comprises a planoconvex lens. Meanwhile, the first field lens <b>123</b><i>h </i>disposed in the first optical path for green lights and the second field lens <b>223</b><i>h </i>disposed in the second optical path for blue lights comprise biconvex lenses to be matched with the relay systems in terms of image-forming characteristic or the like. In addition, let Rg, Rb, and Rr be the radii of curvature of the first through third field lenses, respectively, then an inequality as follows is satisfied: <br />Rr≧Rb>Rg  (6)<br /> In this exemplary embodiment, the third field lens <b>23</b><i>g </i>comprises a planoconvex lens. However, it can include a biconvex lens.

0075In this exemplary embodiment, because an inequality, Rb>Rg, is satisfied, it is possible to make a refractive power of the first field lens <b>123</b><i>h </i>for green lights equal to a refractive power of the second field lens <b>223</b><i>h </i>for blue lights, which makes it possible to correct a chromatic aberration for green and blue. Likewise, because an inequality, Rr≧Rb, is satisfied, it is possible to make a refractive power of the third field lens <b>23</b><i>g </i>for red lights equal to or smaller than a refractive power of the second field lens <b>223</b><i>h </i>for blue lights or the like. The configuration as described above makes it possible to correct a chromatic aberration for respective colors including red, green, and blue, and the respective liquid crystal light valves <b>25</b><i>a, </i><b>25</b><i>b, </i>and <b>25</b><i>c </i>are thereby illuminated by illumination areas of the same size. It is thus possible to project a high-quality image by preventing or reducing a display shadow from being produced.

0076While the invention has been described in line with the first through sixth exemplary embodiments, it should be understood that the invention is not limited to the exemplary embodiments above. For example, in the embodiments above, two fly's-eye systems <b>21</b><i>d </i>and <b>21</b><i>e </i>are used to separate lights from the light source lamp <b>21</b><i>a </i>into plural partial light beams. The invention, however, is also applicable to a projector that does not use such fly's-eye systems, that is, lens arrays. Further, the fly's-eye systems <b>21</b><i>d </i>and <b>21</b><i>e </i>may be replaced with rod integrators.

0077In addition, in the projectors <b>10</b>, <b>10</b>A, <b>10</b>B, <b>110</b>, <b>110</b>A, and <b>110</b>B above, the polarization converting member <b>21</b><i>g </i>is used to convert lights from the light source lamp <b>21</b><i>a </i>to polarized lights in a specific direction. The invention, however, is also applicable to a projector that does not use such a polarization converting member <b>21</b><i>g. </i>

0078Further, the projector includes a front projector that projects an image in a direction in which the user views the projection surface, and a rear projector that projects an image from the opposite side of the direction in which the user views the projection surface, and the structures of the projectors shown in <figref idref="DRAWINGS">FIG. 1</figref> through <figref idref="DRAWINGS">FIG. 6</figref> are all applicable to each type of projector.

0079While this invention has been described in conjunction with the specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, preferred embodiments of the invention as set forth herein are intended to be illustrative, not limiting. There are changes that may be made without departing from the spirit and scope of the invention.